Modern broadcast television (TV) signals for Standard Definition Television (SDTV) generally support three major types of television broadcast standards throughout the world, namely NTSC, PAL, and SECAM. A modern broadcast television signal is received by a television tuner as a sequence of video frames, wherein each video frame includes a series of horizontal scan lines. The television receivers in use when the SDTV standards were developed used an electron beam aimed by a magnet to write each scan line to the screen. In that context, when a broadcast television signal was received by such a television receiver, each horizontal line of video was written sequentially to the screen, one at a time, starting with the first or top horizontal line. When the beam reached the end of the last horizontal line at the bottom of the screen, the beam was turned off in order to allow it to return to the beginning of the next frame (i.e., at the first or top horizontal line again).
A vertical blanking interval (VBI) in an SDTV signal refers to the short period of time during which the beam was turned off and no video would be sent to the television receiver. It was realized that other non-video data could be sent during the VBI period, as long as the television receivers were set up to recognize the data. Accordingly, several types of data (i.e., VBI data) have been transmitted during the VBI period, including Closed Captioning (CC) data, (based on the EIA/CEA-608-B specification), program ratings, and Teletext (based on the BT.653 specification).
However, the advent of television reception on computers has been a challenge in the computer industry. First, processing and displaying high quality video in a computer was a significant obstacle, which has now been adequately resolved. Then, providing high quality audio in synchronization with the video was also an obstacle but it too has been adequately resolved. However, aberrations in VBI signals remain a challenge for ensuring high quality VBI signals (and therefore high quality VBI data). For example, the state of the art requires manual observation of VBI signals on an oscilloscope—an unsatisfactory approach.